Video Transcript
The reaction between ammonia and
boron trifluoride is shown below. What type of bond is formed between
ammonia and boron trifluoride? (A) Ionic bond, (B) covalent bond,
(C) metallic bond, (D) hydrogen bond, (E) coordinate covalent bond.
This question is asking us to
identify the type of bond formed between ammonia and boron trifluoride when they
react, which is this bond, the one between the nitrogen and boron atoms in ammonia
boron trifluoride.
Nitrogen and boron are both
nonmetallic elements. Knowing this can help us eliminate
some of our options. Right off the bat, we can eliminate
answer choice (C) metallic bond, as metallic bonds only involve metals. This type of bonding is found in
sodium metal, silver metal, and iron metal.
We can also eliminate answer choice
(D) hydrogen bond. Hydrogen bonding occurs between
atoms of hydrogen and atoms of a very electronegative element such as nitrogen,
oxygen, and fluorine. Hydrogen bonds occur between
neighboring molecules. The hydrogen of one molecule is
attracted to the lone pair on the highly electronegative atom of the other
molecule. This obviously doesn’t describe the
type of bond between nitrogen and boron.
We can also eliminate answer choice
(A). Ionic bonding typically occurs
between metals and nonmetals. This type of bonding is an
electrostatic attraction between oppositely charged ions. For example, we see this in the
compound sodium chloride.
So now we’re left with two answer
options: covalent bond and coordinate covalent bond. What’s the difference between these
types of bonds? Both covalent bonds and coordinate
covalent bonds involve the sharing of electrons between two nonmetal atoms. Technically, coordinate covalent
bonds are a special type of covalent bonds, but we typically use these two different
terms to refer to two different ways that electrons can be shared.
When a regular covalent bond is
formed, each atom participating in the bond donates one electron. When a coordinate covalent bond is
formed, one atom donates both electrons that make up the bond, and the other atom
doesn’t donate any electrons. Often, a coordinate covalent bond
is represented like a regular covalent bond in a chemical structure, but we might
also see a coordinate covalent bond represented like this. The arrow will point away from the
atom that donated the electrons to form the bond.
We can see that this symbol matches
the one between nitrogen and boron in ammonia boron trifluoride. So this is likely a coordinate
covalent bond, but we can confirm our answer by looking at the Lewis structures for
the reactants, we can see that there is a lone pair on the nitrogen atom. We can also see that boron has no
extra electrons to form bonds with. This means both of the electrons
that make up the bond between nitrogen and boron in ammonia boron trifluoride were
donated by the nitrogen atom. Since nitrogen donated both
electrons to form the bond and boron donated none, so this type of bond is
definitely a coordinate covalent bond.
The type of bond formed between
ammonia and boron trifluoride is answer choice (E) a coordinate covalent bond.
